Atelectasis frequently develops during and after general anesthesia due to factors such as anesthesia-induced diaphragmatic dysfunction, reduced functional residual capacity, altered ventilation-perfusion matching, and surgical positioning. The development of atelectasis has been associated with postoperative hypoxemia and other pulmonary complications.

Lung ultrasound (LUS) has emerged as a reliable, radiation-free bedside imaging modality for the detection and monitoring of atelectasis. LUS allows assessment of lung aeration through standardized ultrasound patterns and scoring systems, enabling dynamic evaluation in the perioperative period.

This is a prospective, observational cohort study designed to compare the incidence and severity of atelectasis in patients undergoing surgery in the supine position versus the prone position under general anesthesia. Adult patients undergoing elective surgical procedures will be enrolled. No experimental intervention will be applied, and all anesthetic and surgical management will follow routine clinical practice.

Lung ultrasound examinations will be performed at predefined time points after induction of anesthesia and before extubation. A standardized lung ultrasound protocol and scoring system will be used to assess lung aeration loss and detect the presence of atelectasis.

The primary outcome of the study is the difference in atelectasis detected by lung ultrasound between supine and prone surgical positions. The secondary outcome is the change in lung ultrasound scores over time.

This study aims to clarify the effects of supine and prone positions on perioperative atelectasis and to support the clinical use of lung ultrasound as a noninvasive monitoring tool in perioperative and anesthetic practice..

Inclusion Criteria:

• Adult patients aged 18 years or older.
• Patients scheduled for elective surgery under general anesthesia.
• Patients undergoing surgery in the supine or prone position.
• Patients able to provide informed consent.

Exclusion Criteria:

• Emergency surgical procedures.
• Pre-existing severe pulmonary disease affecting lung ultrasound assessment.
• Hemodynamic instability requiring urgent intervention.
• Contraindications to lung ultrasound examination.

The study population consists of adult patients aged 18 years and older who are scheduled to undergo elective surgical procedures under general anesthesia. Patients will be evaluated according to surgical positioning (supine or prone) during routine perioperative care.

Individual participant data will not be shared, as this is a single-center observational study conducted for a postgraduate thesis.